1. Field of the Invention
The present invention relates generally to hydraulic valves, and more particularly to improved low flow impedance two- and three-way flow control valves, wherein such two- and three-way flow control valves are optimized for controlling automotive engine heated coolant flow to a host vehicle's radiator, or between the radiator and a bypass line, or even to its heater core.
2. Description of the Prior Art
Flow control valves optimized for operation under conditions of low flow impedance are known in the prior art. One such prior art three-way flow control valve is manufactured by Spartan Peripheral Devices of Vaudreuil, Quebec, Canada. This three-way flow control valve has an axially oriented inlet port and first and second radially oriented output ports. It has a valve spool configured in a generally round thin walled cylindrical manner and has a central web for structural stability and connection to a valve stem. The valve spool is configured with a round outer periphery terminated by first and second orthogonal ends that serve as metering edges.
Fluid conveyed from the inlet port to the first output port merely passes through a first annular orifice formed between the first orthogonal end and a first bulkhead formed as part of an input fitting. On the other hand, fluid conveyed from the inlet port to the second output port must first pass through the valve spool itself and then pass through a second annular orifice formed between the second orthogonal end and a second bulkhead formed as part of a bonnet. For this reason, the valve spool is formed with an internal flow channel between spokes of a web for conveying fluid from a first chamber formed within the first end to a second chamber formed within the second end.
The valve spool is slidingly located within a bore of minimal length located in a third bulkhead formed in the housing for separating the first and second output ports. The valve spool is positioned axially by a valve stem. The valve stem is mounted within a bore formed concentrically within the central web thereby forming a metering assembly comprising the valve spool and valve stem. In addition, the valve stem is slidingly located within a bore located concentrically within the bonnet. Thus, the metering assembly is provided with orthogonal radial position constraints at each of the first bulkhead formed in the housing and second bulkhead formed in the bonnet. A fifth positional constraint is provided by the axial positioning of the metering assembly itself while the sixth or rotational constraint about the axis of motion of the metering assembly is not required for proper functioning of the three-way valve.
Another prior art low flow impedance three-way flow control valve is disclosed in my Provisional U.S. patent application Ser. No. 60/220,340 filed on Jul. 24, 2000 and entitled “Three-Way Flow Control Valve Having Low flow Impedance”. The '340 application discusses a low impedance three-way flow control valve utilized for controlling engine coolant flow between a radiator and a bypass line. In the low impedance three-way flow control valve disclosed in patent application '340, a valve spool apportions fluid flow between axially offset first and second flow receiving annular passages from a central flow distribution chamber. Similarly to the prior art three-way valve described above, the three-way flow control valve disclosed in patent application '340 is configured with an axially oriented inlet port and first and second output ports. However, in the three-way flow control valve disclosed in patent application '340, axially offset first and second flow receiving annular passages are respectively formed as inner portions of the first and second output ports. Further, the housing of the three-way flow control valve disclosed in patent application '340 is formed with its internal bore extending through sealing bulkheads formed on either side of the axially offset first and second flow receiving annular passages as well as a central housing bulkhead.
One negative aspect of either valve construction is practical difficulty in operating their valves with a proportional solenoid. Through extensive testing of the flow control valve disclosed in patent application '340, it has been found that impurities commonly found in automotive engine heated coolant tend to interfere with smooth operation of any juxtaposed sliding surfaces such as those found in any conventional valve or solenoid. This factor appeared to substantially doom the general concept of providing proportional solenoid controlled low flow impedance flow control valves unless a way of eliminating such juxtaposed sliding surfaces could be provided through implementation of improved low flow impedance flow control valves.
Further, it has also been found that the relatively high rate of fluid flow itself tends to interfere with maintenance of an axial force balance on the valve spool. This is because of the formation of vena contractas located slightly downstream of each of the annular orifices. As the axial position of the valve spool and/or the output port pressures vary, reaction forces generated by the vena contractas vary as well. This results in net axial force values being applied to the valve spool. In addition, the presence of the vena contractas means that the effective areas of the first and second annular orifices are significantly less than the apparent annular areas formed by the gaps at either end of the valve spool. The combination of these factors results in a requirement for a much stronger proportional solenoid having an approximately 50% longer stroke length than would be the case if a way of eliminating such vena contracta formation could be found for utilization in the improved low flow impedance flow control valves.
In addition, it has been found difficult to reliably regulate differential fluid flow between the radiator and bypass line as a function of valve spool position. This is because the flow impedance of each of the first and second annular orifices is similar to or even lower than the load impedance presented by either the radiator or the bypass line.
It would be advantageous to provide method and apparatus for controlling engine coolant flow between a radiator and bypass line where no vena contractas are formed with reference to flow control orifices and no juxtaposed sliding surfaces are exposed to engine heated coolant, and further, to provide a method of operation whereby engine coolant flow between the radiator and the bypass line is reliably regulated.